In vehicle applications it is often necessary to provide further gearing between the engine and a vehicle's wheels in addition to the vehicle's main gearbox.
One example of such further gearing can be found on permanent four wheel drive vehicles. Permanent four wheel drive vehicles conventionally have an additional gear selector for selection between high range for normal driving and low range. In low range the vehicle speed is reduced while the engine speed remains much the same and consequently the torque at the wheels is increased for off road driving.
Tracked vehicles may also utilise two ratios, a high ratio for travelling speeds and a low ratio for working speeds. However, conventional primary four speed transmissions do not allow a vehicle to both travel at high speeds (over 70 kph) and to operate at high torque at low speeds (4 kph or less), during applications such as earth moving. To modify such a primary four speed transmission would be expensive.
This invention provides a transmission arrangement that permits both high speed travel and high torque, low speed operation.